1. Technical Field
The present invention relates to a liquid jet apparatus and printing apparatus arranged to print predetermined letters and images by emitting microscopic droplets of liquids from a plurality of nozzles to form the microscopic particles (dots) on a printing medium.
2. Related Art
One example of a printing apparatus currently known in the art is an inkjet printer, which are typically capable of providing high quality color prints at a relatively inexpensive cost. The inkjet printers are widely used, not only in offices, but also by general users along with the widespread popularity of personal computers and digital cameras.
In order to produce a high quality color print in an inkjet printer, it is necessary to print in fine tone. Tone corresponds to the density of each color included in a pixel comprising a liquid dot ejected from the inkjet printer. The size of the liquid dot corresponding to the color density of each pixel is called a tone grade, and the number of the tone grades is called a tone number. A fine tone denotes that there is a large tone number. In order to change the tone grade, it is necessary to modify the drive pulse sent to an actuator provided in the liquid jet head of the inkjet printer. When a piezoelectric element or diaphragm is used as the actuator, since the amount of displacement or distortion of the piezoelectric element increases when the voltage applied to the piezoelectric element increases, the tone grade of the liquid dot can be changed by changing the voltage of the drive pulse.
In one liquid jet head disclosed in Japanese Patent No. JP-A-2003-1824, a plurality of drive pulses with different wave heights are combined and joined before being output to the piezoelectric elements of the nozzles of the same color provided in the liquid jet head. A drive pulse corresponding to the desired tone grade of the liquid dot is selected for every nozzle out of the plurality of drive pulses, and the selected drive pulses are supplied to the piezoelectric elements of the corresponding nozzles. Then droplets of the liquid of different weight are emitted, thereby achieving the desired tone grade.
However, in the inkjet printers currently known in the art, there are difficulties when the phase of the drive pulse is delayed by parasitic inductance, parasitic capacitance, resistance in the wiring of the drive circuit, capacitance of the actuator. Moreover, the amount of phase delay varies in accordance with the number of the actuators driven by the drive pulse. The phase delay in the drive pulse causes delay in the liquid jet emission timing, resulting in variations in the liquid dot forming position (also referred to as a landing position) which leads degradation of the print quality.
Further, when a so-called class-D amplifier, which is a digital power amplifier with little heat generation and power loss, is used as the amplifier of the drive pulses, since the phase characteristic of the low-pass filter varies in accordance with the number of the actuators being driven, and the phase delay increases in accordance with increase in the number of the actuators being driven, and the phase delay described above becomes more apparent.